Flooding caused by some of the Philippines' heaviest rains on record last week submerged more than half of the capital, Manila, turning roads into rivers and trapping tens of thousands of people. In some neighborhoods and surrounding provinces, people stumbled through waist- or neck-deep waters, holding on to ropes strung from flooded houses. The deluge, brought by a monsoon and a tropical storm, dumped more than a month's worth of rain in 24 hours, shutting down offices, banks and schools. The rains killed at least 20 people and forced 200,000 into temporary shelters and 400,000 others into homes of relatives or friends.

Greater Manila, the sprawling, low-lying region of 12 million people, was built on waterways, canals and creeks that have for centuries channeled floodwaters into the sea. But half the narrow waterways and canals that would drain rainwater - constructed and modified during the Spanish colonial period - have been lost, cemented or paved over, experts say. Moreover, much of the "Pearl of the Orient" was lost in heavy bombardment at the end of World War II. The haphazard, poorly planned urban reconstruction has severely strained the city's ability to cope with flooding. Population growth, inadequate infrastructure, corruption, deforestation and even trash build-up also exacerbate the problem.

The recent floods caused an estimated $2.2 billion in damage to infrastructure and agriculture, government officials say.